1. Field of the Invention
The present invention relates to the field of automatic samplers for fluids such as gases and liquids. Such samplers are used, for example, to sample the gas flowing in a natural gas pipeline.
2. Description of the Prior Art
A variety of prior art samplers are of the "clock-wound regulator" type. These devices have a regulator that has an adjusting screw to adjust the discharge pressure of the gas flowing through the device. A clock is mechanically connected to the adjusting screw and as the clock turns, the adjusting screw turns also; but as the adjusting screw is turned down more and more torque is required to turn it due to the build-up of pressure in the sample container. Often during the day, a rise in temperature brings about an increase in pressure of the gas collected in the sample container or cylinder and this pressure reaches the demand pressure of the regulator so that no gas will enter the sample cylinder until the sample cylinder cools off enough for the contained pressure to drop below the demand pressure of the regulator, then more gas will flow into the sample cylinder. This causes erratic sampling between night and day.
In other prior art devices, a deformable cup at the bottom of a cylinder is contacted by a piston that pushes down on the cup. The gas or fluid contained in the cup is forced through a bore running through the piston as the piston pushes against and deforms the cup. Samplers of this type produce a sample of inaccurate size and they require considerable maintenance.